Progressive modulation for downstream access

ABSTRACT

A method, system and computer program for transmitting at least two payloads in a downstream traffic phase of a time-division duplex (TDD) cycle with a single preamble from a headend followed by concatenated payloads without intervening preambles, whereby the payloads are ranked by increasing modulation profiles. The preamble, and concatenated and ordered set of payloads are then transmitted to two or more predetermined customer premise equipments (CPEs).

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/624,546, filed Apr. 16, 2012, the specification of which isincorporated by reference.

FIELD

This disclosure is related to a communication network and moreparticularly to progressive modulation of downstream traffictransmissions in Access Networks that use time-division duplexing (TDD).

BACKGROUND INFORMATION

Multimedia over coax alliance (MoCA) technology for home networks iswell-known and well-understood by someone skilled in the art, as shownand described in www.MoCAlliance.org. MoCA is commonly used to form ahome network, which conveys Ethernet frames among different rooms in thehome over existing coaxial cabling. MoCA's traffic model is known asmultipoint-to-multipoint, because generally every MoCA device in thehome can communicate directly with any other MoCA device in the home.One of the MoCA devices in the home is designated the NetworkCoordinator and becomes responsible for coordinating and scheduling alltraffic on the MoCA home network. MoCA devices form burst transmissionsthat are launched on the coax cables as radio-frequency (RF) signaltransmissions. These transmissions propagate over the coax medium toreach one or more or all of the other MoCA devices in the home network.The Network Coordinator schedules the time and spacing of individualburst transmissions so they do not destructively collide (e.g., overlapin time) at the intended receiver(s). This scheduled arrangement forsharing a communication channel on the coax medium for traffic from andto various endpoints is commonly known as time-division multiple access(TDMA).

Entropic's c.LINK® technology is a coax access system that has someelements similar to MoCA technology for Access Networks. The c.LINKaccess networks have been deployed in China to service multiple-dwellingunits (MDU) (e.g., apartment buildings) over coax cable plants. Theseadaptations include:

-   -   a) locating the Network Coordinator at a headend site;    -   b) locating individual c.LINK devices as customer premise        equipment (CPE);    -   c) scheduling traffic as time-division duplex (TDD);    -   d) scheduling downstream traffic from the headend-to-CPEs, aka        point-to-multipoint;    -   e) scheduling upstream traffic from CPEs-to-headend, aka        multipoint-to-point.

Access Networks are typically deployed by operator/service providers(OSPs) to provide paid high-speed access to the internet and otherOSP-provided services. This includes residential services (such as payTV, telephony, and internet data), as well as business services forbusinesses seeking strict quality of service (QoS) service levelagreement (SLA) contracts including low-latency, low-jitter, andguaranteed throughput. The OSP typically deploys equipment at someheadend (e.g., located in an OSP's central office site, or near someresidential neighborhood, or in the basement of an MDU), whichcommunicates with each of one or more (typically a plurality of)customer premise equipments (CPEs) deployed at endpoint sites such asindividual residences or businesses. The headend can transmit messagesdownstream (DS) over the access network to CPEs (akapoint-to-multipoint), and the CPE endpoints can transmit messagesupstream (US) to the headend in the opposite direction over the accessnetwork (aka multipoint-to-point). Access networks can be based onvarious media types, such as:

-   -   a) Fiber optic cabling;    -   b) Coaxial metallic cabling;    -   c) HFC hybrid fiber and coax cabling (e.g., as identified in        http://www.ieee802.org/3/epoc/public/mar12/schmitt_01_0312.pdf);    -   d) Other metallic cabling (e.g., twisted-pair copper subscriber        loops);    -   e) Other hybrids, such as fiber and twisted-pair; and,    -   f) Wireless media, such over the air transmissions.

The access network medium may contain a cascade of various activecomponents (such as signal amplifiers), as well as lossy passivecomponents (such as splitters or taps), deployed at various fixedlocations in the network. Also, the distances, or medium pathlength,from the headend will generally vary for each CPE. These differencesgenerally result in differing propagation times among the variousbranches in the network, as well as differing arrival amplitudes oftransmitted signals. Consequently, the path between the headend and eachCPE will vary, and the associated signal attenuation, or pathloss, willvary correspondingly. If the pathloss is relatively low, the CPE may becharacterized as nearby the headend. If the pathloss is relatively high,the CPE may be characterized as distant from the headend.

Upstream (US) transmissions are formed and launched by CPEs, but aregenerally not continuous, so upstream traffic from a plurality of CPEsis typically coordinated by the headend in order to ensure that thosenon-continuous or burst transmissions from various CPEs do not collide(overlap in time) and that the headend receiver will observe an orderlysequential arrival of burst transmissions from different CPEs in apredictable order and at predictable times (within some tolerance oftime-jitter). This approach is often called time-division multipleaccess (TDMA).

Some OSPs operate their access network such that upstream traffic anddownstream traffic use different frequencies or wavelengths, enablingtransmissions in both directions, simultaneously and independently(i.e., full duplex). This particular duplexing strategy is calledfrequency division duplex (FDD). The headend has exclusive use andaccess to the downstream frequencies, and the headend cancoordinate/schedule use of the upstream frequencies independently fromthe downstream. FDD is relatively common on access networks today, eventhough FDD operation does incur overheads that reduce spectralefficiency, such as the spectral guard band imposed by inflexible diplexfilters distributed throughout the access network cascade (e.g., toisolate the US and DS traffic from each other).

However, many OSPs desire a different mode of operation: time-divisionduplex (TDD), where a single RF spectral channel-width (or singleoptical wavelength) is being used, and alternating-in-time betweenupstream and downstream (half duplex). TDD's single half-duplex channelalternates between upstream (US) and downstream (DS) traffic, whichimplies the DS link would be unavailable during US traffic, and viceversa. OSPs wish to consider such a mode due to TDD's increasedflexibility (compared to FDD) for adapting to the evolution of future USand DS traffic patterns. One benefit of TDD is that the symmetry orasymmetry of the US and DS capacities is a relatively simple (andrealtime) adjustment of the duty-cycle phasing of the TDD Cycle. Use ofTDD in the Access Network enables a more flexible way for OSPs toeasily, quickly and inexpensively adjust the relative throughputcapacity of the upstream and downstream directions within a singlespectral allocation. Whereas, FDD requires paired spectral allocationstypically established by inflexible diplex filters distributedthroughout the access network cascade. For a given total aggregatespectral allocation, TDD's single spectral allocation can be made aswide as the sum of FDD's paired allocations, enabling TDD's burstdatarate capability in either direction being approximately double thatof FDD in either direction (for symmetric US and DS FDD allocations). Amore extensive discussion of TDD is available at the website located athttp://www.ieee802.org/3/epoc/public/may12/barr_01_0512.pdf.

Some access networks currently deploy TDD technology, such as c.LINKAccess, which is typically used to service MDUs in China. In addition,there are new access network technologies currently under development(e.g., in the IEEE 802.3bn EPoC Task Force, and in ITU-T G.fast) whichare being designed to leverage the inherent flexibility of TDD.

TDD operation has certain overheads that reduce temporal efficiency. Forexample, it is necessary for the headend scheduler to avoid collisionsin the TDD mode of operation by segregating the upstream traffic fromdownstream traffic with a time gap, such as an inter-phase gap (IPG)between TDD phases. An IPG may include time intervals for transmissionsto complete their propagation from transmitter(s) to intendedreceiver(s), time for the medium to sufficiently quiesce (if necessary)after reception(s), and time for destination transceiver(s) to switch(if necessary) from receive to transmit mode. As shown in FIG. 1 , thesequential combination of any two adjacent TDD phases (i.e., a singledownstream phase 12 plus a single upstream phase 16) is called a TDDCycle 10. There are IPGs 14 between phases. TDD Cycles 10 with durationon the order of 1 millisecond are commonly deployed in access networksemploying TDD (although longer or shorter durations can be used). In theTDD mode of operation, it is common for each transmitter to prepend apreamble signal at the beginning of each of its transmissions. Thesepreambles include reference signals which can be useful to facilitatereceivers in detecting and acquiring the physical layer (PHY) parametersrequired to properly decode the transmission, such as gain,frequency-offset and timing information. The time intervals thatpreambles consume on the medium, are generally accounted as overhead forTDD. In the upstream, the PHY of each CPE typically starts its bursttransmission with a preamble as shown in FIG. 2 , where preamble 18 istransmitted first, followed by payload 20 (message-information oruser-data carrying portion) of the transmission.

These upstream preambles facilitate the headend receiver to detect andacquire the PHY layer parameters which in general are unique to eachindividual CPE device. For example, the differing pathloss from each CPEto the headend generally results in differences in arrival amplitude atthe headend from each CPE's upstream transmissions. These differences inarrival amplitude correspond in general to different SNRs as received atthe headend. Anyone skilled in the art knows that the capacity for achannel to carry information is closely related to this received SNR andis discussed in the website located athttp://en.wikipedia.org/wiki/Channel_capacity.

When a CPE is nearby the headend, the pathloss may be low, the arrivalamplitude may be high, and the SNR may be high, yielding a higherchannel capacity to or from that particular CPE. Conversely, when a CPEis distant from the headend, the pathloss may be high, the arrivalamplitude may be low, and the SNR may be low, yielding a lower channelcapacity to or from that particular CPE. The headend, being aware ofthese differences in reception, generally schedules each CPE to transmitits payload information using a modulation profile that corresponds tothe particular SNR that can be received from that particular CPE. Forexample, the headend might schedule a higher modulation profile fornearby CPEs, and a lower modulation profile for distant CPEs.

Modulation Profile (MP) generally refers to various combinations ofmodulation density with forward error correction, or MCS modulation andcoding scheme, as discussed in the website located athttp://en.wikipedia.org/wiki/Modulation_and_coding_scheme. DifferentModulation Profiles are generally chosen to adapt communication signaltransmissions to the particular conditions experienced on thecommunications channel. A high modulation profile generally correspondsto a relatively high-density modulation (e.g., 1024-QAM, being higherthan 256-QAM), and/or a relatively high coding rate for forward errorcorrection. A lower modulation profile corresponds to a relativelylow-density modulation (e.g., 256-QAM, being lower than 1024-QAM),and/or a relatively lower coding rate for forward error correction. Ahigh modulation profile carries more information bits per second (or persymbol) than a lower modulation profile. However, high modulationprofiles are more difficult to receive and decode (i.e., lowreceptivity), requiring better channel conditions (e.g., higher SNR)than would otherwise be required with a lower modulation profile that iseasier to receive and decode (i.e., having higher receptivity).

Summarizing, for distant CPEs whose channel conditions are insufficient,the headend must resort to transmitting lower modulation profiles andsuffer the lower bits-per-second information rate. It would be betterfor the OSP if the headend could transmit high modulation profileswhenever possible, enabling nearby CPEs whose channel conditions aresufficiently good to realize the higher bits-per-second informationrate. However, preambles represent the overhead associated with theheadend changing modulation profiles, and these overheads work againstthe benefits that otherwise could be realized by using differentmodulation profiles.

SUMMARY

The presently claimed Progressive Modulation invention improves theefficiency of downstream traffic transmissions in Access Networks thatuse TDD time-division duplexing. By concatenating payloads in rank orderof progressively increasing modulation profile, the headend no longerneeds to transmit intervening preambles before each new modulationprofile.

The following presents a simplified summary of one or more embodimentsin order to provide a basic understanding of some aspects of suchembodiments. This summary is not an extensive overview of the one ormore embodiments, and is intended to neither identify key or criticalelements of the embodiments nor delineate the scope of such embodiments.Its sole purpose is to present some concepts of the describedembodiments in a simplified form as a prelude to the more detaileddescription that is presented later.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed method and apparatus, in accordance with one or morevarious embodiments, is described with reference to the followingfigures. The drawings are provided for purposes of illustration only,and merely depict examples of some embodiments of the disclosed methodand apparatus. These drawings are provided to facilitate the reader'sunderstanding of the disclosed method and apparatus. They should not beconsidered to limit the breadth, scope, or applicability of the claimedinvention. It should be noted that for clarity and ease of illustrationthese drawings are not necessarily made to scale.

FIG. 1 is a depiction of a typical TDD cycle.

FIG. 2 shows a typical PHY preamble and PHY payload.

FIG. 3 shows the preferred embodiment of the claimed invention.

The figures are not intended to be exhaustive or to limit the claimedinvention to the precise form disclosed. It should be understood thatthe disclosed method and apparatus can be practiced with modificationand alteration, and that the invention should be limited only by theclaims and the equivalents thereof.

DETAILED DESCRIPTION

State of the art for downstream TDD transmission is quite similar tothat described for upstream: The headend transmits a preamble tofacilitate the CPE receiver, followed by a payload whose modulationprofile is chosen to adapt to the particular channel conditions for theparticular intended CPE receiver. In the downstream case, the directionof the traffic is reversed, and the channel properties may in general bedifferent from the upstream case, such as the pathloss (which may becharacterized as distance), SNR, channel capacity, and receptivity, andthese properties may vary per CPE. A preamble is broadly defined as toother well know methods having substantially the same purpose, such as:Header, PHY Header, Start Marker, PHY Start marker, Pilot Tones, PilotCarriers or the like. Also, the preamble may carry some informationabout how the subsequent payload is to be decoded (e.g., some indicationof the modulation profile). When the headend needs to send a differentpayload to a different CPE, it transmits another preamble first,followed by the payload adapted to the channel conditions for thatparticular CPE. The second preamble is needed to facilitate the secondCPE receiver, because, although the second receiver would be able todetect and acquire the PHY layer parameters from the first preamble, thesecond CPE receiver is in general unable to receive and decode the firstpayload because it uses some other modulation profile, so the secondreceiver loses track of the headend's transmission. Thus, the secondpreamble is needed for the second CPE receiver to re-detect andre-acquire the signal from the headend before the second payloadarrives.

As shown in FIG. 3 , the presently claimed invention teaches headend 30to concatenate two or more of the downstream payloads, where each mayhave different modulation profiles, without requiring interveningpreambles to be transmitted. Headend 30 transmits a single preamble 38at the start of downstream phase 46, followed by the concatenatedpayloads 32, 34, 36. Although this disclosure in the examples described,only three payloads are described, this disclosure is intended toinclude any number of payloads. If two such payloads are concatenated byheadend 30, then the presently claimed invention eliminates the need forthe headend to transmit a second intervening preamble between them. Ifthree such payloads are concatenated by the headend, then the presentlyclaimed invention eliminates the need for the headend to transmit asecond and third intervening preamble. A similar result is obtained for4 or more such payloads that are concatenated by the headend. Headend 30may concatenate in this fashion for as long as it has downstream dataavailable for transmission to CPEs, or until reaching the end ofdownstream phase 46 of the current TDD Cycle 48. The headend wouldrestart the process for each downstream phase of subsequent TDD Cycles.

An example of the claimed invention advances the state of the artbecause the amount of overhead consumed by downstream preambles isreduced, thereby making more channel-time available per downstream phase46 for headend 30 to schedule information-carrying payloads.Furthermore, the overhead associated with employing a high ordermodulation profile for nearby CPEs is reduced, enabling the headend tomore readily achieve the higher information-rates for those CPEs. Thisreduction in preamble overhead can be quite significant if manypreambles are eliminated, such as the case when the headend is activelyservicing a large number of CPEs and/or when there are many relativelyshort payloads to be transmitted downstream that are latency-sensitive.Making the downstream transmissions more efficient, the claimedinvention enables the headend to sustain a higher downstream throughputcapacity. Alternatively, the headend can schedule less time fordownstream phases 46, thereby allowing for a greater volume of upstreamtraffic in upstream phases 50 to be transmitted, or allowing forshortened TDD Cycles 48 to reduce latency.

An example of the claimed invention, as shown in FIG. 3 , teachesheadend 30 to concatenate payloads in rank order of progressivelyincreasing modulation profile. That is, a first payload 32 of aconcatenated set of payloads has the lowest modulation profile of theset, and a last payload 36 of a concatenated set has the highestmodulation profile in the set, and payloads in the middle 34 of aconcatenated set have intermediate modulation profiles. As a verysimplistic example, the payloads intended for the most distant CPEs 40are transmitted by headend 30 shortly after preamble 38, followed bypayloads intended for mid-range CPEs 42, then finally ending withpayloads intended for the most nearby CPEs 44. This rank ordering byProgressive Modulation Profile is important, since it enables all of theintended CPEs to not only detect and acquire the PHY layer parametersfrom single leading preamble 38, but also to keep track of the headend'stransmissions up to and including the particular payloads intended forthose CPEs. Each CPE is typically informed by headend 30 beforehandwhich payloads within downstream phase 46 are intended for it (e.g.,Headend 30 can inform this via a scheduling message(s) sent to CPEsbeforehand, such as a well-known media access plan (MAP) message).

For example, consider the headend's downstream transmission from theperspective of the most distant CPE 40: Most distant CPE 40 receivessingle leading preamble 38, from which it detects and acquires the PHYlayer parameters required to properly decode the subsequent payload,such as gain, frequency-offset and timing information. Very firstpayload 32 arriving after single leading preamble 38 is the payload withthe lowest modulation profile (e.g., intended for the most distant CPE40, for example 256-QAM). Consequently, this most distant CPE 40 is ableto accurately track the headend's transmission for the duration of firstpayload 32, and accurately receive and decode the payload informationbits intended for this most distant CPE 40. Next to arrive at mostdistant CPE 40 is second payload 34 in the concatenated set of payloads.Second payload 34 might possibly have the same modulation profile asfirst payload 32, but in general would have a higher modulation profilethan first payload 32 (e.g., being intended for the next most distantCPE 42 to receive downstream traffic in the concatenated set, forexample 512-QAM). This rank order by Progressive Modulation Profile isimposed by headend 30 according to the claimed invention. Second payload34, having higher modulation profile, is more difficult for the mostdistant CPE 40 to track and decode accurately, and, in general, may notbe accurately decoded. However, most distant CPE 40 has already receivedand decoded first payload 32 to which it was intended, and there is nolonger any need for most distant CPE 40 to track or decode any morepayloads in downstream phase 46 of current TDD Cycle 48.

Now consider the same example, but from the perspective of most nearbyCPE 44: Most nearby CPE 44 receives single leading preamble 38, fromwhich it detects and acquires the PHY layer parameters required toproperly decode subsequent payloads, such as gain, frequency-offset andtiming information. First payload 32 arriving after single leadingpreamble 38 is the payload with the lowest modulation profile (e.g.,intended for most distant CPE 40). Consequently, most nearby CPE 44 iseasily able to accurately track the headend's transmission for theduration of first payload 32. Next to arrive at most nearby CPE 44 issecond payload 34 in the concatenated set of payloads. Second payload 34might possibly have the same modulation profile as first payload 32, butin general would have a higher modulation profile than the firstpayload. Nevertheless, most nearby CPE 44 is able to continue accuratelytracking the headend's transmission for the duration of second payload34. Similarly, most nearby CPE 44 is able to continue accuratelytracking all the subsequent payloads in downstream phase 46, even astheir modulation profiles increase progressively. Finally, last payload36 in the concatenated set, having the highest modulation profile of all(e.g., 1024-QAM), arrives at most nearby CPE 44. Last payload 36 isspecifically intended for most nearby CPE 44, so it can be accuratelytracked and decoded.

While various embodiments of the disclosed method and apparatus havebeen described above, it should be understood that they have beenpresented by way of example only, and should not limit the claimedinvention. Likewise, the various diagrams may depict an examplearchitectural or other configuration for the disclosed method andapparatus. This is done to aid in understanding the features andfunctionality that can be included in the disclosed method andapparatus. The claimed invention is not restricted to the illustratedexample architectures or configurations, rather the desired features canbe implemented using a variety of alternative architectures andconfigurations. Indeed, it will be apparent to one of skill in the arthow alternative functional, logical or physical partitioning andconfigurations can be implemented to implement the desired features ofthe disclosed method and apparatus. Also, a multitude of differentconstituent module names other than those depicted herein can be appliedto the various partitions. Additionally, with regard to flow diagrams,operational descriptions and method claims, the order in which the stepsare presented herein shall not mandate that various embodiments beimplemented to perform the recited functionality in the same orderunless the context dictates otherwise.

Although the disclosed method and apparatus is described above in termsof various exemplary embodiments and implementations, it should beunderstood that the various features, aspects and functionalitydescribed in one or more of the individual embodiments are not limitedin their applicability to the particular embodiment with which they aredescribed. Thus, the breadth and scope of the claimed invention shouldnot be limited by any of the above-described exemplary embodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

A group of items linked with the conjunction “and” should not be read asrequiring that each and every one of those items be present in thegrouping, but rather should be read as “and/or” unless expressly statedotherwise. Similarly, a group of items linked with the conjunction “or”should not be read as requiring mutual exclusivity among that group, butrather should also be read as “and/or” unless expressly statedotherwise. Furthermore, although items, elements or components of thedisclosed method and apparatus may be described or claimed in thesingular, the plural is contemplated to be within the scope thereofunless limitation to the singular is explicitly stated.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, can be combined in asingle package or separately maintained and can further be distributedin multiple groupings or packages or across multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

What is claimed is: 1-6. (canceled)
 7. A method comprising: receiving apreamble; receiving a message that comprises a plurality of payloads,wherein: the plurality of payloads are arranged in an order ofincreasing modulation profile, and there are no intervening preamblesbetween adjacent payloads of the plurality of payloads; identifying apayload, of the plurality of payloads, according to the preamble; anddecoding the identified payload according to the preamble.
 8. The methodof claim 7, wherein: the method is performed by a node in a network, andthe node receives the preamble and the message from a coordinator of thenetwork.
 9. The method of claim 7, wherein: the method is performed by anetwork node, and the network node receives the preamble and the messagefrom a headend node.
 10. The method of claim 7, wherein: the preamblecomprises physical (PHY) layer parameters for the plurality of payloads.11. The method of claim 7, wherein: there is no intervening informationbetween adjacent ones of the plurality of payloads.
 12. The method ofclaim 7, wherein: the method is performed by a node, the node is aclosest node to a transmitter of the message, and the identified payloadis any payload of the plurality of payloads.
 13. The method of claim 7,wherein: the plurality of payloads are arranged in an order ofincreasing degrees of Quadrature Amplitude Modulation (QAM).
 14. Amethod, comprising: receiving a first message identifying a payload of aplurality of payloads, wherein the plurality of payloads are arranged inan order of increasing modulation profile; receiving a second messagecomprising a preamble and the plurality of payloads; determining,according to the preamble, how to decode the identified payload; anddecoding the identified payload.
 15. The method of claim 14, wherein:the method is performed by a node in a network, and the node receivesthe preamble and the payload from a coordinator of the network.
 16. Themethod of claim 14, wherein: the method is performed by a network node,and the network node receives the preamble and the payload from a headend node.
 17. The method of claim 14, wherein: the preamble comprisesphysical (PHY) layer parameters for the plurality of payloads.
 18. Themethod of claim 14, wherein: there is no intervening information betweenadjacent ones of the plurality of payloads.
 19. The method of claim 14,wherein: the method is performed by a node, the node is a closest nodeto a transmitter of the message, and the identified payload is a lastpayload of the plurality of payloads.
 21. The method of claim 14,wherein: the plurality of payloads are arranged in an order ofincreasing degrees of Quadrature Amplitude Modulation (QAM).
 21. Amethod, comprising: receiving a message from a transmitting node, themessage comprising: a preamble, and a plurality of payloads followingthe preamble, wherein the plurality of payloads are arranged in an orderaccording to a distance from the transmitting node and there are nointervening preambles between adjacent ones of the plurality ofpayloads; identifying a payload of the plurality of payloads;determining, according to the preamble, how to demodulate the identifiedpayload; and demodulating the identified payload.
 22. The method ofclaim 21, wherein the plurality of payloads are arranged in an order ofdecreasing distance from a transmitting node.
 23. The method of claim21, wherein: the method is performed by a node in a network, and thenode receives the preamble and the payload from a coordinator of thenetwork.
 24. The method of claim 21, wherein: there is no interveningpreamble between adjacent ones of the plurality of payloads.
 25. Themethod of claim 21, wherein: the preamble comprises physical (PHY) layerparameters for the plurality of payloads.
 26. The method of claim 21,wherein: there is no intervening information between adjacent ones ofthe plurality of payloads.